SP pinwheel


The Strategic Goal of Stormwater Management is designed to continue mitigation of flooding across Cook County through a proactive, equitable stormwater management program, including implementation of gray and green infrastructure, enforcement of the Watershed Management Ordinance (WMO), and acquisition of flood prone property. 


The MWRD Stormwater Program utilizes a variety of strategies in these efforts.

SW Program


Stategic Plan logo The Tunnel and Reservoir Plan (TARP)

The Tunnel and Reservoir Plan (TARP) system includes 110 miles of deep, large-diameter tunnels and three expansive reservoirs; it is designed to reduce flooding, improve water quality in Chicago area waterways, and protect Lake Michigan’s drinking water supply from pollution caused by combined sewer overflows (CSOs). TARP captures and stores combined stormwater and sewage that would otherwise overflow from sewers and pollute local waterways during heavy rainfall events. As capacity becomes available, this stored water is pumped from TARP to water reclamation plants (WRPs) for treatment prior to discharge to the waterways. 

TARP comprises three distinct tunnel and reservoir systems:  

  • The Upper Des Plaines TARP System is located in the northwest suburbs and is the smallest of the three. It has captured nearly all of the CSOs within its service area since becoming fully operational with the completion of the Majewski Reservoir in 1998.  

  • The Calumet TARP System serves the south side of Chicago and south suburbs and was completed in 2015 with the addition of the Thornton Composite Reservoir.  

  • The Mainstream and Des Plaines TARP System is the largest, serving most of Chicago and several suburbs to the north, west, and southwest. It includes the partially completed McCook Reservoir. The completion of Stage 1 of the McCook Reservoir in 2017 greatly reduced the amount of CSOs in this service area.  While this system already captures the most CSO due to its large service area, Stage 2 of the McCook Reservoir is still under construction, so it has not reached its full potential in terms of percentage of CSO captured.  


CSO Combined Chart


The amount of CSOs captured is directly related to the amount of rainfall received. From 2017 through 2021, the total MWRD TARP system captured over 153 billion gallons of CSOs. During the same period, the Calumet and Upper Des Plaines Systems have consistently captured all or nearly all CSOs, while the Mainstream/Des Plaines System is expected to further increase percentage capture after completion of Stage 2 of the McCook Reservoir.

The TARP Status Report presents construction progress, cost, and State/Federal grant and revolving loan funding information on the Tunnel and Reservoir Plan (TARP).


Stategic Plan logo Stormwater Infrastructure

Through a variety of engineered solutions, both green and gray, and flood-prone property acquisitions, MWRD’s Stormwater Management Program addresses both regional and local flooding problems throughout Cook County. MWRD has made significant investments in developing over 140 capital stormwater projects since it assumed the authority for stormwater management in 2004. These projects, which range in both size and scope, provide flood protection for thousands of homes, businesses, and critical infrastructure. Click here to view a map of the MWRD's Stormwater Infrastructure Projects.


Stategic Plan logo Environmental Justice

To support equitable access to MWRD services and benefits, the MWRD has identified low- to moderate-income areas that may be more susceptible to flooding.  MWRD prioritizes efforts to mitigate stormwater impacts and outreach to encourage participation in our stormwater partnership programs.  Efforts to identify and eliminate barriers to participation are a key focus of the Strategic Plan, and the MWRD is committed to equitable access to a variety of stormwater solutionsThe following map illustrates the locations of stormwater management projects overlaid with data from the Department of Housing and Urban Development for low- and moderate-income areas.


DIA Projects Map


Stategic Plan logo Stormwater Partnership Opportunities

Local governments and public agencies within MWRD’s corporate boundaries can apply to become partners to fund and build stormwater management projects. These include our Stormwater Partnership Program, which provides funding and technical support to address urban flooding through traditional stormwater detention and conveyance improvements, and our Flood-Prone Property Acquisition Program which assists in the acquisition of flood-prone structures and conversion to open space. 

Through our Green Infrastructure Partnership Opportunity Program (GIPP) MWRD encourages and supports implementing green infrastructure (GI), which includes a range of engineered installations that store, infiltrate, and/or evaporate stormwater, thereby mimicking the natural water cycle.


Bioswale GI Image

Since 2014, MWRD has partnered with dozens of local partner agencies to fund GI projects such as rain gardens, bioswales/bioretention areas, permeable pavement systems, and rain water harvesting systems. MWRD solicits applications from various governmental agencies within its jurisdiction for GI projects on an annual basis. More information about our GIPP and other MWRD Stormwater Partnership Opportunities can be found here.


GI Graph

Through 2021, the District has partnered with numerous local agencies on 69 green infrastructure projects to  install over 12 million gallons of retention capacity to capture stormwater runoff that would otherwise have drained into local sewers, thereby minimizing the potential for basement backups and combined sewer overflows.


Stategic Plan logo Watershed Management Ordinance (WMO)

WMO Fourth Quarter Report 2021

The MWRD adopted the Watershed Management Ordinance (WMO) in 2014 to establish uniform, minimum countywide comprehensive stormwater management regulations for development in Cook County. The MWRD tracks stormwater storage volume constructed under WMO permits in conjunction with development under the WMO, and reports periodically on these quantities. In the above WMO report, the first table provides information broken down by quarters, showing the number of WMO permits issued, total area of proposed development approved under WMO permits, and quantity of volume control through green infrastructure, stormwater detention, and compensatory storage to be constructed under approved permits.

One of the goals of the WMO is to protect existing and new development by minimizing the increase of stormwater runoff beyond that experienced under existing conditions and by reducing peak stormwater flows. Stormwater detention and volume control are effective ways to accomplish the goal and are required for many developments in Cook County. 

An additional goal of the WMO is to ensure that future development in the floodplain does not adversely affect floodplain environments or increase the potential for flood damage. The WMO requires compensatory storage to be provided to offset any fill placed in the regulatory floodplain as a result of development.

The second table in the above WMO report lists each of the permits that have been issued through 2021 that have either created or utilized offsite stormwater management facilities. The WMO allows for a portion of the required stormwater detention and volume control to be provided in offsite facilities, under certain conditions. The MWRD tracks available supply sites and their utilization by demand sites under WMO permits. These tables highlight the MWRD’s ongoing efforts to ensure effective stormwater management measures are incorporated into new development and redevelopment throughout Cook County, in accordance with Strategic Goal #2. 

Additional information regarding the WMO can be found here

Stategic Plan logo Stormwater Inundation Mapping Application (SWIMA)

The Stormwater Inundation Mapping Application (SWIMA) is a tool developed by the MWRD to provide general flood risk information for Cook County. The application allows users to view the 100-year inundation areas and the modeled water surface elevations that were originally developed as part of the MWRD's Detailed Watershed Planning (DWP) program as well as the regulatory floodplain/floodway information from the FEMA Flood Insurance Study. Letter of Map Revisions (LOMRs) and Letter of Map Amendments (LOMAs) can also be viewed in this application. SWIMA can be found here.

Please note that this application is for general information regarding floodplains and inundation areas. Do not scale dimensions off this application. Official FEMA Flood Insurance Study information can be obtained from FEMA. 

If you have questions about this application, please contact the MWRD's Engineering Department - Stormwater Management Section, at 312-751-5600, or via e-mail at stormwater@mwrd.org.


The information presented here is meant to provide context for this Strategic Goal and serves as a baseline for efforts going forward. We are still in the early stages of implementation; as we progress further through the Strategic Plan, we will provide more information as it becomes available.


Return to Main Strategic Plan Page